A recurring problem in patients with impaired function of the respiratory system is that the volume of air-exchanging lung parenchyma is reduced. This may be due to either edema, lung collapse and/or other factors. If a volume of air-transporting parenchyma/airways, comprising for example the main bronchi, trachea, and upper airways is maintained, the volume of air-exchanging parenchyma decreases relative to that of the air-transporting parenchyma/airways. In situations of increased need for CO2 removal, a ventilatory contribution may be hampered if a dead space, or dead volume, in an air-transporting parenchyma/airways and in a respiratory circuit for a mechanical ventilator, becomes abnormally large relative to a proportion of the lungs with intact air-exchanging parenchyma. Consequently, CO2 removal is hampered and arterial CO2(PaCO2) may increase. This causes the tidal volume and ventilation to increase in order to maintain a tolerable level of arterial pressure (PaCO2).
Until today, efforts have been made to minimize dead space, or dead volume, introduced in the respiratory circuit of mechanical ventilators. However actual tubes, for example endotracheal tubes, and other devices of conventional mechanical ventilators used to administer respiratory assist to a patient use single lumen designs and contribute to dead space ventilation. For that reason, CO2 removal cannot be optimized.
Previous attempts to improve CO2 removal from endotracheal tubes include multi-lumen designs aimed at introducing an air flow through a side lumen to eliminate CO2 from a main lumen. An example of such design may be found in U.S. Pat. No. 5,291,882. The proposed approach, which uses parallel lumens, does not eliminate completely the volume of air re-breathed by the patient during inspiration. Thus the proposed approach reduces, but does not optimize the CO2 removal and minimize the CO2 re-breathing problem. Moreover, problems of dynamic hyperinflation due to constant inspiratory flow has also complicated this approach. Other approaches using tube lumens with valve functions may increase risk of occlusion.
Therefore, there is a need for improvements leading to further reduction or elimination of dead space induced by the respiratory circuit of a mechanical ventilator.